scholarly journals The Low Speed Wave Resistance Theory Imposing Accurate Hull Surface Condition

1979 ◽  
Vol 1979 (146) ◽  
pp. 27-34
Author(s):  
Yoshihiro Shimomura ◽  
Takamune Kitazawa ◽  
Takao Inui ◽  
Hisashi Kajitani
Keyword(s):  
Surface Condition ◽  
Wave Resistance ◽  
Low Speed ◽  
Resistance Theory

Waves and wave resistance of thin bodies moving at low speed: the free-surface nonlinear effect

1975 ◽  
Vol 69 (2) ◽  
pp. 405-416 ◽  
Author(s):  
G. Dagan
Keyword(s):  
Free Surface ◽  
Froude Number ◽  
Surface Condition ◽  
Perturbation Expansion ◽  
Wave Resistance ◽  
The Body ◽  
Thin Body ◽  
Two Dimensional ◽  
First Order ◽  
Flow Past

The linearized theory of free-surface gravity flow past submerged or floating bodies is based on a perturbation expansion of the velocity potential in the slenderness parameter e with the Froude number F kept fixed. It is shown that, although the free-wave amplitude and the associated wave resistance tend to zero as F → 0, the linearized solution is not uniform in this limit: the ratio between the second- and first-order terms becomes unbounded as F → 0 with ε fixed. This non-uniformity (called ‘the second Froude number paradox’ in previous work) is related to the nonlinearity of the free-surface condition. Criteria for uniformity of the thin-body expansion, combining ε and F, are derived for two-dimensional flows. These criteria depend on the shape of the leading (and trailing) edge: as the shape becomes finer the linearized solution becomes valid for smaller F.Uniform first-order approximations for two-dimensional flow past submerged bodies are derived with the aid of the method of co-ordinate straining. The straining leads to an apparent displacement of the most singular points of the body contour (the leading and trailing edges for a smooth shape) and, therefore, to an apparent change in the effective Froude number.

Radiation and diffraction of water waves by a submerged sphere at forward speed

1988 ◽  
Vol 417 (1853) ◽  
pp. 433-461 ◽  
Keyword(s):  
Water Waves ◽  
Velocity Potential ◽  
Surface Condition ◽  
Wave Resistance ◽  
The Body ◽  
Legendre Functions ◽  
Forward Speed ◽  
Submerged Sphere ◽  
Exciting Forces ◽  
Similar Equation

A submerged sphere advancing in regular deep-water waves at constant forward speed is analysed by linearized potential theory. A distribution of sources over the surface of the sphere is expanded into a series of Legendre functions, by extension of the method used by Farell ( J . Ship Res . 17, 1 (1973)) in analysing the wave resistance on a submerged spheroid. The equations governing the velocity potential are satisfied by use of the appropriate Green function and by choosing the coefficients in the series of Legendre functions such that the body surface condition is satisfied. Numerical results are obtained for the wave resistance, hydrodynamic coefficients and exciting forces on the sphere. Some theoretical aspects of a body advancing in waves are also discussed. The far-field equation of Newman ( J . Ship Res . 5, 44 (1961)) for calculation of the damping coefficients is extended, and a similar equation for the exciting forces is derived.

The Effect of a Surface Layer of Viscous Fluid on the Wave Resistance of a Thin Ship

1974 ◽  
Vol 18 (04) ◽  
pp. 265-271
Author(s):  
E. O. Tuck
Keyword(s):  
Surface Layer ◽  
Free Surface ◽  
Viscous Fluid ◽  
Gravity Wave ◽  
Oil Spills ◽  
Surface Condition ◽  
Wave Resistance ◽  
Surface Layers ◽  
Free Surface Condition

A Modification to the gravity-wave free-surface condition is suggested, to account for dissipative properties of thin surface layers of material such as broken-up ice, slush, or oil spills. A corresponding correction to michell's wave-resistance integral is established, and computations are carried out for a parabolic strut.

Unsteady Wave-Making Resistance of an Accelerating Ship

2020 ◽  
Author(s):  
Mingxin Li ◽  
Zhi-Ming Yuan ◽  
Ronald W. Yeung
Keyword(s):  
Surface Condition ◽  
Oscillation Amplitude ◽  
Solution Procedure ◽  
Wave Resistance ◽  
Boundary Integral ◽  
Ship Model ◽  
Implicit Finite Difference ◽  
Force Components ◽  
Unsteady Effects ◽  
Nonlinear Free Surface

Abstract To measure the resistance of a ship in a towing tank, the target speed of the ship model is achieved by towing the model from the rest at a given acceleration imposed by the carriage. The fluctuations in resistance are generated because of the impulse effects during rapid acceleration. Such acceleration effects in deep water have been studied by previous works [1–3]. In shallow water, the unsteady effects are expected to be stronger, making the fluctuating resistance persisting longer. In order to predict the unsteady waves and to estimate the unsteady oscillating components in the wave resistance, a numerical method based on 3D unsteady potential-flow theory was developed. An implicit finite-difference algorithm coupled with an iterative boundary integral-equation solution procedure was used to deal with the unsteady linear and nonlinear free-surface condition. The results showed that both the acceleration intensity and water depth have a significant effect on the oscillation amplitude of the unsteady wave resistance as well as other force components. Findings of these computations and comparative evaluation of experimental observation are made where relevant. The findings in the present work can be applied to provide guidance for using the appropriate settings, e.g., magnitude and duration of carriage acceleration, when conducting ship-model resistance tests.

Ultrasonic Evaluation of Surface Condition of Road Material with Low-Speed Measurement

2017 ◽  
Vol 2017 (0) ◽  
pp. OS0413
Author(s):  
Yuki OGI ◽  
Naoya NISHIMURA ◽  
Taichi NISHIDA ◽  
Shotaro SUGIURA
Keyword(s):  
Surface Condition ◽  
Low Speed ◽  
Ultrasonic Evaluation ◽  
Speed Measurement

scholarly journals The management of fluid and wave resistances by whirligig beetles

2009 ◽  
Vol 7 (43) ◽  
pp. 343-352 ◽  
Author(s):  
Jonathan Voise ◽  
Jérôme Casas
Keyword(s):  
Aquatic Insects ◽  
Water Surface ◽  
High Speed ◽  
Wave Resistance ◽  
Low Speed ◽  
Fluid Resistance ◽  
Air Water Interface ◽  
Large Container ◽  
Leg Kinematics ◽  
Resistance Forces

Whirligig beetles (Coleoptera: Gyrinidae) are semi-aquatic insects with a morphology and propulsion system highly adapted to their life at the air–water interface. When swimming on the water surface, beetles are subject to both fluid resistance and wave resistance. The purpose of this study was to analyse swimming speed, leg kinematics and the capillarity waves produced by whirligig beetles on the water surface in a simple environment. Whirligig beetles of the species Gyrinus substriatus were filmed in a large container, with a high-speed camera. Resistance forces were also estimated. These beetles used three types of leg kinematics, differing in the sequence of leg strokes: two for swimming at low speed and one for swimming at high speed. Four main speed patterns were produced by different combinations of these types of leg kinematics, and the minimum speed for the production of surface waves (23 cm s −1 ) corresponded to an upper limit when beetles used low-speed leg kinematics. Each type of leg kinematics produced characteristic capillarity waves, even if the beetles moved at a speed below 23 cm s −1 . Our results indicate that whirligig beetles use low- and high-speed leg kinematics to avoid maximum drag and swim at speed corresponding to low resistances.

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